old animefag here, I haven't watched a series of this genre with interest since Darker Than Black.
Frieren has a poetic lightness in dealing with even serious and complex subjects, and although they are not new themes in the media, I find them narrated and developed with such frankness and simplicity, that they are clear and easy to relate to
it is not pretentious, in fact, it is even the opposite: everything is very clear, without particular twists of "morally grey" characters, or other tropes of modern narrative.
I find it refreshing and delightful.
she is also a beautiful female character, both in appearance and writing